Leaves alternate or opposite, petiolate or sessile, entire or ± serrate; stipules usually small and persistent, rarely foliaceous or deciduous.

Inflorescences

Inflorescence of single flowers in the leaf axils or, more rarely, terminal racemes or axillary racemes or clusters; pedicels articulated.

Flowers

Flowers zygomorphic.

Calyx

Sepals almost equal, without a basal appendage.

Corolla

Petals unequal, the anterior one smaller, or usually much larger, than the others, unguiculate, with a short basal spur.

Stamens

Stamens with filaments of varying length, free or ± coherent, the two anterior ones (and rarely also the lateral ones) with free or coherent appendages which extend into the spur and may secrete nectar ("spur-appendages"); anthers free or coherent, with a thin dorsal prolongation of the connective ("connective-appendage").